In the speaker system of the delay array system, a number of speaker units arranged linearly or arranged on a plane output the same sound signal while giving a slightly different delay time to the signal such that these sound signals arrive at a certain point (focal point) in a space simultaneously, so that acoustic energy around the focal points is enhanced by the in-phase addition and as a result the sharp directivity, i.e., the sound beam is generated in the direction of the focal point.
Then, when the above delay process is applied to each channel of the multiple channels respectively and then signals on all channels are added together before they are output to the speaker unit, output signals on the multiple channels provide the sound beams each having a different directivity on each channel respectively because the speaker unit and the space are the substantially linear system.
Accordingly, a large sound volume can be provided to only a hearing-impaired person by enhancing the directivity in the particular direction (Patent Literature 1), two persons can listen simultaneously to different contents respectively by giving the different directivity to sounds of two different contents respectively (Patent Literature 2), or a surround sound field can be generated by causing the sound beams on the multichannels containing the surround to reflect partially from the walls and generating the virtual sound sources (Patent Literature 3).
FIG. 3 is a view showing a situation in which virtual sound sources are generated near the walls by directing plural beams at any walls of the room to reflect from there and thus a multichannel surround sound field is generated.
In FIG. 3, 31 is a listening room, 32 is a video system, 33 is an array speaker, 34 is a listener, 35 is a wall surface on the left side of the listener, 36 is a wall surface on the right side of the listener, and 37 is a wall surface on the rear side of the listener. Here, explanation will be made under the assumption that the five-channel reproduction is carried out hereunder. The sound signal is generated forward from the array speaker 33 based on the center (C) channel signal, a virtual FL channel sound source 38 is generated based on the front left (FL) channel signal by controlling the beam to direct it at the wall surface 35 on the left side of the listener, and a virtual FR channel sound source 39 is generated based on the front right (FR) channel signal by controlling the beam to direct it at the wall surface 36 on the right side of the listener. Also, a virtual RL channel sound source 40 is generated based on the rear left (RL) channel signal by controlling the beam to direct it at the rear-side wall surface 37 from the left-side wall 35, and a virtual RR channel sound source 41 is generated based on the rear right (RR) channel signal by controlling the beam to direct it at the rear-side wall surface 37 from the right-side wall 36.
In this manner, the signals on respective FL (front left), FR (front right), RL (rear left), and RR (rear right) channels are shaped into the beams by giving the sharp directivity to them, and then the listener 34 is caused to feel the sound sources in the wall direction based on the beams reflected from the walls. Therefore, the surround sound field can be generated by the virtual sound sources while using one array speaker provided on the front side.
Meanwhile, the frequency band whose directivity can be controlled by the array speaker is decided physically by the array profile. In other words, the wavelength that is longer that a full width of the array (low frequency) or the wavelength that is shorter than a pitch between the speaker units (high frequency) cannot be controlled by the array speaker. Thus, actually a small-sized wide-range speaker is employed as the speaker unit to control the high frequency band to some extent. Since the array speaker cannot control the low frequency band unless a full width of the array is expanded even if the user tries to control the directivity of the low frequency band, a number of speaker units are needed. As a result, the system in which the low frequency is not shaped into the beam and is output separately has been proposed (Patent Literature 3).
FIG. 4 is a block diagram showing a configuration of the array speaker system that does not shape the low frequency band into the beam. In FIG. 4, 33 is the above array speaker that is constructed by a plurality (n) of speaker units 33-1 to 33-n. 
As shown in FIG. 4, the signals on respective center (C), front left (FL), front right (FR), rear left (RL), and rear right (RR) channels are input into the subband filters provided to correspond to respective channels. Each subband filter is composed of a set of a high-pass filter (HPF) and a low-pass filter (LPF). The signals on respective channels are divided into a signal (high frequency component) having a frequency higher than a crossover frequency (crossover frequency) that passes through HPFs 51-1 to 51-5 selectively and a signal (low frequency component) having a frequency lower than the crossover frequency that passes through LPFs 52-1 to 52-5 selectively respectively.
The low frequency components of the signals on respective channels, which are passed through LPFs 52-1 to 52-5, are added by an adder 53, and then an added signal is input into a signal adjusting portion (ADJ portion) constituted by a gain controlling portion 54-6, a frequency characteristic correcting portion 55-6, and a delay circuit 56-6. Here, the level and the frequency characteristic of the signal are corrected and a resultant signal is delayed in a predetermined time.
Also, the high frequency components of the signals on respective channels, which are passed through HPFs 51-1 to 51-5, are input into a signal adjusting portion constituted by gain controlling portions 54-1 to 54-5, frequency characteristic correcting portions (EQs) 55-1 to 55-5, and delay circuits 56-1 to 56-5, which are provided to correspond to respective channels. Here, the level and the frequency characteristic of the signals are corrected respectively and resultant signals are delayed in a predetermined time respectively. Then, signals are input into directivity controlling portions (Dir C) 57-1 to 57-5 provided to correspond to respective channels respectively, so that signals on respective channels being output to the speaker units 33-1 to 33-n of the array speaker 33 to have the directivity shown in FIG. 3 are generated. Delay circuits and gain setting portions corresponding to respective speaker units 33-1 to 33-n are provided to the directivity controlling portions 57-1 to 57-5, where an amount of delay is set to direct the beam in the direction allocated to the channel and a window factor is a multiplied to reduce the side lobes. Thus, signals being output to respective speaker units 33-1 to 33-n are generated.
The signals output from the directivity controlling portions 57-1 to 57-5, which have a higher frequency than the crossover frequency of each channel respectively and correspond to respective speaker units, and a signal output from the delay circuit 55-6, which has a frequency lower than the crossover frequencies of all channels, are input into adders 58-1 to 58-n provided to correspond to respective speaker units, and are added respectively.
The signals output from the adders 58-1 to 58-n are amplified by power amplifiers 59-1 to 59-n provided to correspond to respective speaker units 33-1 to 33-n, and are output from the corresponding speaker units 33-1 to 33-n. 
In this manner, the signals whose frequency is lower than the crossover frequency respectively are not shaped into the beam on all channels and then output, while the signals whose frequency is higher than the crossover frequency respectively are shaped into the beam as shown in FIG. 3 and then output.
Patent Literature 1: JP-A-11-136788
Patent Literature 2: JP-A-11-27604
Patent Literature 3: WO01/023104 (JP-T-2003-510924)